Here is what I meant: the results of 500 procs in fact shows it with
272-304(<500) real cores, the program's running time is good, which is
almost five times 100 procs' time. So it can be handled very well. Therefore
I guess OpenMPI or Rocks OS does make use of hyperthreading to do the job.
But with 600 procs, the running time is more than double of that of 500
procs. I don't know why. This is my problem.